Mid Sweden University

In this work we present a simple printed moisture sensor fabricated using electronic inks on a multilayer paper structure. The sensor is based on a Carbon-Zinc type energy cell and provides power to a readout electronic circuit when activated by moisture. The sensors are based on a number of our filed patents according to which the sensor is used for both event detection and as a power source for the processing electronics. Typical applications are moisture and leakage detection in buildings, water pipe lines, smart packages and health care systems such as smart incontinence sensors. As the detector is triggered, it powers up an electronic circuit (polymer based or silicon based) that starts communication with the alarm server. In the simplest systems a sound or a light alarm is started to alert the user. In this work we present a characterization of some critical parameters of the sensor such as power driving capability, linearity, internal memory effects and saturation. In addition, we examine a specific application, when sensor is used as defrosting alarm for surveillance of frozen articles during transport.

In this work we present a study on the performance of printed touch sensor fabricated using conductive ink on paper substrates. The sensor system is intended to add values in surveillance of packages or in interactive point-of-purchase displays. The printed sensor changes its capacitance when it is touched or manipulated. The capacitance variations are readout using either a wireless or wired communication link. The most advanced system will utilize RFID or ZigBee readout technology while the simplest systems utilize a simple analog wire solution. The sensor technology has been developed to be easily integrated into high quality prints targeting applications such as large area touch sensitive commercial stands, flat keyboards at point-of-purchase and touch and manipulation surveillance in logistic chains.

The paper presents a concept where pairs of ordinary RFID tags are exploited for use as remotely read moisture sensors. The pair of tags is incorporated into one label where one of the tags is embedded in a moisture absorbent material and the other is left open. In a humid environment the moisture concentration is higher in the absorbent material than the surrounding environment which causes degradation to the embedded tag’s antenna in terms of dielectric losses and change of input impedance. The level of relative humidity or the amount of water in the absorbent material is determined for a passive RFID system by comparing the difference in RFID reader output power required to power up respectively the open and embedded tag. It is similarly shown how the backscattered signal strength of a semi-active RFID system is proportional to the relative humidity and amount of water in the absorbent material. Typical applications include moisture detection in buildings, especially from leaking water pipe connections hidden beyond walls. Presented solution has a cost comparable to ordinary RFID tags, and the passive system also has infinite life time since no internal power supply is needed. The concept is characterized for two commercial RFID systems, one passive operating at 868 MHz and one semi-active operating at 2.45 GHz.

This work presents a study on the performance of printed low cost moisture sensors fabricated using conductive ink on paper substrates. The sensors are intended to add value to the surveillance of packages. Two different kinds of sensors are evaluated and characterized. The two sensors have similar geometrical shapes, but different measuring principles are employed. The first sensor is measuring the moisture content in cellulose based substrates, while the second is measuring high levels of relative humidity in the surroundings. The sensors have been developed so that they can be integrated into Radio Frequency Identification (RFID) systems for surveillance in logistic chains. A laboratory setup of a RFID tag with sensor capability based on an ordinary passive RFID tag has been shown.